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Internetworking
Hussain Ali, [email protected]
Department of Computer Engineering King Fahd University of Petroleum and
MineralsDhahran, Saudi Arabia
What is Internetworking ?
Internetworking stands forconnectivity and communication
between two or more networks.
dropping the “s” from Networks.
How is Internetworking Achieved ?
Cables and physical interfaces (physical
connectivity)
Protocols, management and applications
needed to support user (Internetworking)
Motivation for Internetworking
Overcome distance limitations and protocol
differences for more effective sharing of data
and resources
Productive communication between people
across a single network or multiple networksEmail, newsgroups, mailing lists, live conferencing
Components of an Internetwork
Campus NetworkLocally connected users in a building or group of
buildings Wide Area Networks (WANs)
Distant campuses connected together usually through connection providers such as the phone company
Remote ConnectionsLinking branch offices and mobile users to a
corporate campus
Campus Networks
A campus is a building or group of buildings
all connected into one enterprise network that
consists of many local area networks.
The distinct characteristic of a campus is that
the company network owns the physical wires.
Campus network topology is primarily LAN
technology connecting all the end systems
together.
Campus networks generally use LAN
technologies such as Ethernet, Token Ring,
FDDI, Fast Ethernet, and ATM.
Wide Area Networks
WAN communication occurs between
geographically separate areas.
In enterprise internetworks, WANs connect
campuses together.
When a local end station wants to
communicate with a remote end station,
information must be sent over one or more
WAN links.
WAN services are provided through the
following 3 primary switching technologies:Circuit Switching
Packet Switching
Cell Switching
Remote Connection
Remote connections link single mobile users and branch offices to a local campus.
Typically a branch office is a small site that has few users and needs a low bandwidth WAN connection.
These small sites or single users, seldom need to remain connected 24 hours a day.
Remote connections are generally dial-up links or low bandwidth dedicated WAN links.
Trends in LAN/WAN Integration
Today, most of the computing power resides on the desktop, and this power is growing.
Distributed applications are increasingly bandwidth hungry.
Voice communications have increased significantly.
All of this is driving towards an integration of LANs and WANS under one roof.
In the LAN, bandwidth is free and connectivity is limited only by hardware.
In the WAN, bandwidth is an excessive cost. The existence and development of bandwidth
sensitive traffic such as voice and real-time video has forced a requirement of better and more predictable LAN and WAN performance.
Interaction of Different Networks
1. LAN-to-LAN 2. LAN-to-WAN 3. WAN-to-WAN4. LAN-to-WAN-to-LAN
Host 802.5LAN
MR
SNA WAN
X.25 WAN
MR
B
MR
MR
802.3 LAN802.4 LAN802.3 LAN
Host
Host
Host Host
B: Bridge MR: Multi-protocol router
HostHostHostHost
Devices that interconnect LANs are known as relays and operate at one layer of OSI model
There are four common types of relaysRepeater: at physical layer (bits)Bridge: at data-link layer (frames)Router: at network layer (packets)Gateways: at transport and higher
layers (protocols)
Relays
Repeater (Hub)
Overcomes restrictions caused by single segment usage such as number of users, cable length.
Amplifies or regenerates weak signals . Extends cable length Can connect LANs of a similar type but which
use different media. Provides simple connection between adjacent
LANs at the expense of increased network congestion
Use of Repeaters for a Multi-segment LAN
Repeater
Segment A
Segment B
Station
PrinterStation
Stations
File Server
Bridge Interconnects two or more LANs (either similar
or dissimilar) at the MAC level. Capable of deciding whether or not to forward
frame. Creates an extended network and keeps local
traffic off. Can make minor changes to frame header. Does not inspect or modify the network layer
packets inside frames.
Characteristics of Bridges
Routing Tables Filtering Forwarding Learning Algorithm
Routing tableContains one entry per station of network to
which bridge is connected.Is used to determine the network of
destination station of a received packet. Filtering
Is used by bridge to allow only those packets destined to the remote network.
Packets are filtered with respect to their destination and multicast addresses.
Forwarding: the process of passing a packet from one network to another.
Learning: the process by which the bridge learns how to reach stations on the internetwork.
Operation of a LAN bridge from 802.3 to 802.4
802.3 CSMA/CD 802.4 Token bus
Host A
LLC
MAC
Host B
Physical
MAC
LLC
NetworkBridge
802.3Packet
802.3Packet
802.4
Packet
Packet
802.4Packet
802.4Packet
Packet
Packet
Packet
802.3
802.3
802.4
Physical
Network
Transparent Bridges The first IEEE 802 bridge is a transparent
bridge or spanning tree bridge. People wanted to have complete transparency:
when a site with multiple LANs buys bridges designed to the IEEE standard, just plug connectors into bridges. So,no need for hardware/software changes,no setting of address switches,no downloading of routing tables or
parameters.
A transparent bridge accepts every frame transmitted on all the LANs to which it is attached.
A BD
CF
H
G
E
LAN 1 LAN 2 LAN 3
LAN 4
BridgeBridge
Topology can change dynamically. There must be only one path of bridges and
LANs between any two segments in the bridged LAN
Bridges must support Spanning Tree Protocol if network contains loops.
Have the advantage of being easy to install Use only a subset of topology. Are chosen by the CSMA/CD and token bus.
Source Routing Bridges Token ring people chose the source routing
bridge. Transmitter, or source, of frame in source
routing specifies which route the frame is to follow.
Every machine in the network knows, or can find, the best path to every other machine; discovery frame is used.
Sender knows whether or not the destination is on its own LAN.
Issue TransparentBridge
Source Routing Bridge
Orientation Connectionless Connection-oriented
Transparency Transparent tohosts
Not transparent
Configuration Automatic Manual
Routing Suboptimal Optimal
LocatingDestinations
Backward learning Discovery frames
Failures Handled bybridges
Handled by hosts
Complexity In the bridges In the hosts
Comparison of Bridges
Router
Provides a more intelligent servicemakes a decision as to the best way to
deliver a packet from source to destinationmay fragment packets to meet packet size
requirements of LANsare slower than bridges
Permits translation between different address domains such as addresses of IEEE 802 LAN and X.25
Connects dissimilar networks, provided that end-systems use a common network layer protocol, such as IP.
Unlike bridge, router receive only those packets addressed to it by either a user machine or another router.
Select the best route. The question of who owns, operates, and
maintains a router arises especially when two networks belong to independent organizations.
Full Router and Two Half-Routers
Buffer
Net 1 to internet
Net 2 to internet
Network 1 Network 2
internet to Net 1
internet to Net 2
Network 1 Network 2
Net 1 tointernet
Net 2 tointernet
internetto Net 2
internetto Net 1
Machine owned jointly by bothnetworks
Full Router:
Two-HalfRouters:
Disadvantages of Routers
Routersare protocol-dependent devices that must
understand the protocol they are forwarding.can require a considerable amount of initial
configuration.are relatively complex devices, and generally are
more expensive than bridges.
Advantages of Routers
Routers provide sophisticated routing, flow
control, and traffic isolation are configurable, which allows network
manager to make policy based on routing decisions
allow active loops so that redundant paths are available
Gateway
Connects end-systems whose host protocols have varying degrees of difference
Transport gateways make a connection between two networks at the transport layer.
Application gateways connect two parts of an application in the application layer, e.g., sending email between two machines using different mail formats
Connect two networks above the network layer of OSI model.
Are capable of converting data frames and network protocols into the format needed by another network.
Provide for translation services between different computer protocols.
Routers versus Bridges
Addressing Routers are explicitly addressed. Bridges are not addressed.
AvailabilityRouters can handle failures in links, stations,
and other routers.Bridges use only source and destination
MAC address, which does not guarantee delivery of frames.
Message Size » Routers can perform fragmentation on
packets and thus handle different packet sizes.
» Bridges cannot do fragmentation and should not forward a frame which is too big for the next LAN.
Forwarding» Routers forward a message to a specific
destination.» Bridges forward a message to an outgoing
network.
Priority» Routers can treat packets according to
priorities» Bridges treat all packets equally.
Error Rate
» Network layers have error-checking algorithms that examines each received packet.
» The MAC layer provides a very low undetected bit error rate.
Security
» Both bridges and routers provide the ability to put “security walls” around specific stations.
» Routers generally provide greater security than bridges because
–they can be addressed directly and
–they use additional data for implementing security.
Brouters: Bridging Routers
Combine features of bridges and routers. Capable of establishing a bridge between two
networks as well as routing some messages from the bridge networks to other networks.
Are sometimes called (Layer 2/3) switches and are a combination of bridge/router hardware and software.
Network Connectivity Devices Entry-level Hubs
Interconnect PCs in a single network segmentSimple stand-alone device that provides a starting point
cost-effective connectivity for many organizations.
Network Connectivity Devices (contd.)
Stackable HubsLet you start small and grow your network at your own
pace.Are connected by flexible expansion cables, and once
stacked together, function as one hub.Manageable as one logical unit.
Network Connectivity Devices (contd.)
Chassis HubBig iron box that can contain a variety of network
modules.It has a power supply, a high speed backplane, and
expansion slots for plug-in Hub modules.
Network Connectivity Devices (contd.)
Workgroup switchesLow-end network devices that aggregate multiple
shared segmentsUse switching technologyTypically deployed at the desktop levelEthernet, Token-Ring, or ATM
Network Connectivity Devices (contd.)
Workgroup switchesLow-end network devices that aggregate multiple
shared segmentsUse switching technology.Typically deployed at the desktop level.
Network Connectivity Devices (contd.)
Backbone switchesHigh-end network devices deployed at the core of the
network.Use switching technology.Aggregate data from Hubs and Workgroup switches.Typically accept various networking options.
Network Connectivity Devices (contd.)
RoutersPerform routing of packets among LANs.Provide most effective way of segmenting the network.Move data by finding the best path from the sender to
the receiver.Suitable for organizations with many large LANs.